The present exemplary embodiment relates generally to a method and system for document processing. More specifically, the present exemplary embodiment relates to a digital scanning velocity control method and system.
Digital copiers are well known. Whereas a traditional “analog” copier in effect directly takes a photograph of the image desired to be copied, in a digital copier, an original image on an input sheet is recorded as digital data, and the digital data is used to create a print which is a copy of the original image. The original image is typically recorded by an array of photosensors, such as in a charge-coupled-device (CCD), while the printing step is typically carried out by familiar “ink-jet” technology, or by digital “laser printer” rendering in a xerographic apparatus.
Between the recording of the original image and the output of a resulting print, the image data can be processed and manipulated, such as through digital image processing, in any number of ways. Chief among these ways is alteration of the placement of the image relative to a print sheet on which the image is ultimately rendered: the placement of the image further involves consideration of hardware-related factors such as the start-of-scan control in a scanning laser which creates a latent image on a photoreceptor in a xerographic printer, or the precise control of a moving printhead in an ink-jet apparatus. Another aspect of processing image data between recording and printing relates to the magnification of the image.
Ideally, in a basic case, it is desirable that a copy output by a digital copier be as similar to the original image as possible, particularly in the aspects of placement of the image relative to the edge of the print sheet, as well as magnification of the printed image relative to the original. In a conventional digital reproduction device, a document or image is scanned by a digital scanner, which converts the light reflected from the document into electrical charges representing the light intensity from predetermined areas (or pixels) of the document. The pixels of image data are processed by an image processing system, which converts the pixels of image data into signals that can be utilized by the digital reproduction machine to recreate the scanned image. In other words, the image processing system provides the transfer function between the light reflected from the document to the mark on the recording medium.
Image sensor arrays typically comprise a linear array of photosensors, which raster scan an image bearing document and convert the microscopic image areas viewed by each photosensor to image signal charges. Following an integration period, the image signal charges are amplified and transferred as an analog video signal to a common output line or bus through successively actuated multiplexing transistors.
For high-performance image sensor arrays, one design includes an array of photosensors of a width comparable to the width of a page being scanned, to permit one-to-one imaging generally without the use of reductive optics. In order to provide such a “full-width” array, however, relatively large silicon structures must be used to define the large number of photosensors. A preferred technique to create such a large array is to align several butted silicon chips, each chip defining a small linear array thereon. In one design, for example, an array is intended to comprise up to twenty silicon chips, butted end-to-end, with each chip having 372 active photosensors spaced at 600 photosensors per inch.
One measure of the performance of a reproduction machine is how well the copy matches the original. With respect to input imaging terminals using constant velocity document transports or platen scanning devices, the scanning velocity is critical to high quality image reproduction. Many current implementations, however, may create velocity errors that lead to image quality defects, since the imaging sensor to paper speed cannot be guaranteed.
Therefore, it is desirable to utilize a system and method for detecting and correcting motion quality issues associated with digital scanners.